I think you have to ask yourself if Nintendo want kids discovering swear words on their platform by googling acronyms that people use on it. And yes, bastards is a swear word as far as many parents are concerned. The system has parental controls, but that doesn't extend to policing individual user decisions like what they decide to call themselves. Kids are going to encounter bad language sooner or later, but the Nintendo ecosystem is much cleaner than others, unless you're playing something like Rocket League, in which case, the internet anonymity equation applies. I had a friend banned on PlayStation a few years back for calling himself futher mucker. Companies just don't want you doing stuff like that..
For me, allowing BLM to stand is good enough for me to show good will towards that particular political cause, you just know that someone out there is absolutely frothing that Nintendo allow people to put BLM in their nicks. It's not like they're censoring the movement. For things like ACAB, I get why they don't want it - I don't need them to allow a free for all in users nicknames. I'm not sure naming yourself ACAB in Nintendo games is going to change the world anyway, its a reductive statement that is more true in some parts of the world than others and kids are by and large born good. Abhorrent views are almost always socialised. It's the older generation and the voting generation who need to wake up and make positive change in the world.. and if they can't, hopefully when they shuffle off, the generations coming up behind them will.
